The present invention relates to inlet valves for appliances and in particular to water inlet valves for domestic appliances such as, for example, ice makers and humidifiers. Appliances of this type commonly employ an electrically actuated water inlet valve for supplying water to a receptacle in response to energization from a programmer timer. The electrical actuation is usually accomplished by energizing a solenoid having a armature operable to effect movement of the valving member.
Where solenoid actuated water inlet valves are employed for appliances, two types of such valves have been found useful: namely, a pilot operated valve and a directly actuated valve.
In instances where relatively low flow rates are required for a particular appliance application there is insufficient pressure differential across the diaphragm of a pilot operated valve to stroke the main valve open sufficiently to prevent trapping of foreign particles on the valve seat.
The amount of main valve member or poppet, stroke of such a valve at very low flow rates may be only a small fraction of a millimeter and consequently the flow velocity is high across the main valve seat. The higher flow velocities encountered with such a small stroke or opening of the main valve member tend to move all foreign particles entering the valving chamber to the valve seat where they are trapped by the aforesaid small opening formed by the poppet lift from the valve seat.
In field service, the trapping of particles at the valve seat has been found to cause an accumulation of particles and a resultant build-up or deposits of foreign material on the valve seat. These deposits have prevented sealing of the valve upon closing and this has caused the valve to fail by not being able to shut off flow.
It has therefore been found necessary, for such low flow rate applications, to employ a directly actuated solenoid valve to effect proper opening of main valving member.
In low flow rate applications where a directly actuated solenoid valve has been employed, it has been found that the magnetomotive force required to effect direct movement of the valving member by the solenoid armature becomes substantially greater than that required for a pilot operated valve. In order to provide the increased magnetomotive force additional ampere-turns are required in the coil, which increases the amount of copper in the coil and thus results in increased manufacturing costs.
In those applications where higher flow rates are required for the particular appliance, the high velocity exit flow reduces the static pressure and this creates sufficient pressure forces on the main valving member to enable a pilot operated valve to be employed. The magnetomotive force required for armature actuation of a pilot operated valve is quite low, and thus a smaller less costly coil may be employed in the solenoid.
Thus, it has long been desired to find a way or means of employing a low cost pilot operated pressure differential actuated solenoid inlet valve for low flow rate applications in appliances. In particular it has been desired to provide a solenoid type pilot operated water inlet valve for low flow rate applications where the main valving member strokes sufficiently to prevent trapping and build-up of foreign particles on the valve seat.